Gulf War illness (GWI), a multisymptom condition resulting from service in the Persian Gulf War (GW), is one of the most prominent health issues affecting GW Veterans. Insomnia is common in Veterans with GWI. For example, all of the Veterans in our current VA Merit GW project who meet the Centers for Disease Control and Prevention (CDC) case definition for GWI and 64% of the Veterans who meet the Kansas GWI case definition (which, unlike the CDC4 case definition, has exclusionary conditions), have Insomnia Severity Index scores indicative of clinical insomnia. Furthermore, insomnia severity and subjective sleep quality are significantly correlated with GWI symptom severity, as assessed by the Kansas Gulf War Military History and Health Questionnaire (r's >0.45, p's <0.01) in these Veterans. This suggests that: (1) sleep disruption adversely affects systems (e.g., cognition, neuroendocrine, and autonomic) that likely play an important role in GWI, and (2) there are reciprocal links between sleep quality, sleep-wake regulation, and fatigue, a common symptom of individuals with GWI and insomnia. Study co-investigators Drs. Neylan and Maguen have previously shown Cognitive Behavioral Therapy for Insomnia (CBT-I) to be efficacious for reducing insomnia and non-sleep posttraumatic stress disorder (PTSD) symptoms. Because current PTSD symptom severity is also strongly correlated with insomnia and GWI symptom severity in Veterans in our current VA Merit project (r's >0.45, p's <0.01), we hypothesize that CBT-I will similarly reduce insomnia and non-sleep GWI symptoms in GW Veterans. The proposed study will test this hypothesis in a pilot trial of CBT-I for sleep and non-sleep GWI symptoms. Insomnia is commonly under-recognized and untreated. For example, none of the Veterans in our current VA Merit GW project who likely have clinical insomnia have heard of or have been referred to CBT-I by their VA healthcare providers. This suggests that, despite the VA's national roll-out of CBT-I, Veterans with GWI are not the target population for CBT-I. Although CBT-I has been studied in a number of disorders comorbid with insomnia, we contend that examining CBT-I in the context of GWI is important because: 1) insomnia is common in Veterans with GWI, 2) untreated insomnia can lead to significant medical and psychiatric morbidity; 3) there is still no evidence-based treatment for GWI nearly 25 years after the end of the Gulf War. Furthermore, our proposal to modify CBT-I for telephone delivery, which studies have found to be as efficacious as face-to-face CBT-I, is significant because it will extend this effective form of behavioral sleep therapy to the Veterans with GWI who have physical and/or functional impairments that may limit their ability to participate in treatments that require regular clinic visits. The proposed study will employ a two-arm randomized controlled trial to investigate the efficacy of telephone- delivered CBT-I for sleep and non-sleep GWI symptoms in 64 Veterans with GWI according to the CDC and Kansas case definitions and insomnia disorder according to DSM-5 research diagnostic criteria. Half of the Veterans will be randomized to CBT-I and half to a treatment-as-usual control group. Veterans randomized to the control group will have the option of receiving telephone-delivered CBT-I upon completion of the study. The primary outcomes will be effect sizes based on within-group comparisons of pre-to-post-treatment change and maintenance of treatment effects at 6 months in the group randomized to CBT-I. In light of the RAC's 2014 recommendation that the first priority of federal Gulf War illness research must be the identification of effective treatments to improve the health of Gulf War Veterans, the proposed trial may be an important first step towards identifying a non-pharmacologic treatment with relatively low burden and few known risks that could benefit some of the estimated 175,000 Veterans with GWI injured during their military service.